The disclosure relates in general to a brushless DC motor drive apparatus. In particular, the present disclosure relates to a brushless DC motor drive apparatus without Hall sensor, and providing functions of automatic power shutoff and restoration.
Among electronic device, it is common to include a cooling fan, to prevent overheating and resulting burnout. Upon overheating, the fan is normally initialized to lower the temperature, and dissipate excess heat from the system.
Conventionally, the fan is driven by a motor. A brushless DC motor (BLDC) is conventionally utilized, owing to easy maintenance, good controllability, and efficient performance. Not only in low power applications such as motors in hard drives and compact disk (CD) drives, but also in high power applications such as the motor apparatus in electric cars, brushless DC motors provide advantages such as high efficiency, stable rotation, high torsion, endurance, and easy maintenance.
FIG. 1 shows a circuit schematic of a conventional brushless DC motor driver, in which a drive circuit 100 of brushless DC motor includes a first winding L1, a second winding L2, a capacitor C1, transistors Q1, Q2, Q3, Zener diodes ZD1, ZD2, ZD3, and resistors R1, R2, R3. The first winding L1 may be a supplementary winding, and the second winding L2 may be a power winding, both of which magnetically excite and drive the rotor to rotate, via the switching operation and alternated current directions of the drive circuit 100.
First State
When a constant voltage source provides a current, the voltage potential at node “a” is high, and the voltage potential at node “b” is relatively low, across both ends of the first winding L1 simultaneously. Low voltage potential results at the base of the transistor Q2, subsequently switched off, such that no current flows through the first winding L1.
Concurrently, the base of the transistor Q3 is at a high voltage potential, such that the transistor Q3 becomes conductive, a current passes through the transistor Q3 from the second winding L2 to ground. The second winding L2 exerts control over a stator generating an induced magnetic field so as to drive the rotor to rotate at a predetermined angle via the induced magnetic field. For example, rotating 90° counterclockwise.
Second State
When the rotor reaches the predetermined angle, the first winding L1 detects a state of power generation, and correspondingly generates a reverse inductive signal (e.g., reverse voltage), so that the voltage potential at node “a” is low, and the voltage potential at node “b” is relatively high. Positive voltage is applied to the base of the transistor Q2, in turn switching the transistor Q2 on current through the resistor R2 and the transistor Q2 to ground. Thus, the base of the transistor Q3 is brought to a low voltage potential, and the transistor Q3 is switched off, such that there is no current through second winding L2. Though no magnetic field is induced across the stator the rotor continues rotating in the same direction, returning to the first operating condition subsequently, alternating between operating conditions.
However, the above-mentioned conventional drive circuit has several problems to resolve. When the fan is blocked by a foreign object such as an obstacle, the rotor is stopped immediately. In the absence of tangential magnetic force, the first winding L1 becomes inactive. As the result, the transistor Q2 remains off, with no current through the first winding L1. Because the conventional drive circuit does not have the function of cutting the power when the fan is blocked, a continuous current is provided through the second winding L2 and the transistor Q3 to ground. Heat generated at second winding L2 causes possible damage to the brushless DC motor and the entire system.
In addition, the conventional circuit cannot spontaneously restart the circuit operation to drive the rotor even if the obstacle is removed. To restore circuit operation, it is necessary to disconnect the power supply then reconnect the brushless DC motor, which presents considerable inconvenience.